1. Field of the Invention
The present invention relates to an optical scanning device and an image forming apparatus equipped with the optical scanning device, such as a digital copying machine and a laser printer.
2. Description of the Related Art
Various types of optical scanning devices for scanning a surface of an object to be scanned, such as a photoreceptor, have been developed and put into practical use. Of these optical scanning devices, those included in image forming apparatuses, such as a laser printer, have different configurations in most cases, even if the optical scanning devices are produced by the same manufacturer. This is because layouts of the image forming apparatuses equipped with the optical scanning devices are different from one another.
For example, in a digital copying machine shown in FIG. 16A, a paper feeding unit 201, a scanner 202, and an imaging engine unit 203 are respectively arranged at the bottom, the top, and the center of the digital copying machine, and a copy receiving tray 206 to which paper is discharged is located on one of the sides of the digital copying machine. In this layout, it is necessary to convey paper fed from the paper feeding unit 201 to a transfer unit that is located below a photosensitive drum 204. Therefore, an optical scanning device 205 is inevitably arranged above the photosensitive drum 204 in terms of a process configuration and procedures of electrophotographic processing. The digital copying machine contains the optical scanning device 205, so that an overall width of the digital copying machine needs to be larger than the same for the optical scanning device 205 (with minimizing the overall width of the digital copying machine as much as possible). Consequently, the optical scanning device 205 needs to include a reflection mirror for reflecting a scanning beam to shorten the overall width of the optical scanning device 205.
In a laser printer shown in FIG. 16B, a paper feeding unit 301 is arranged at the bottom of the laser printer, and an imaging engine unit 303 is arranged on top of the paper feeding unit 301. In this layout, a paper path is longitudinally arranged on one of the sides of the laser printer, and paper is conveyed through the paper path and discharged onto a copy receiving tray 306 that is located on the top of the laser printer. Therefore, an optical scanning device 305 is inevitably arranged on the (slightly downward) lateral side of a photosensitive drum 304 in terms of a process configuration and procedures of electrophotographic processing. Then, an interface device 307 is arranged adjacent to the optical scanning device 305, so that the optical scanning device 305 needs to include a reflection mirror for reflecting a scanning beam to minimize a size of the optical scanning device 305.
In a full-color printer shown in FIG. 16C, a paper feeding unit 401 is arranged at the bottom of the full-color printer, and an imaging engine unit 403 is arranged on top of the paper feeding unit 401. The imaging engine unit 403 includes a plurality (in this case, four) of photosensitive drums 404 and a plurality (in this case, four) of optical scanning devices 405 corresponding to each of the photosensitive drums 404 respectively. In this layout, a paper path is longitudinally arranged on one of the sides of the full-color printer, and paper is conveyed through the paper path and discharged onto a copy receiving tray 406 that is located on the top of the full-color printer. Therefore, the optical scanning devices 405 are inevitably arranged lateral to the photosensitive drums 404. In this case, the optical scanning devices 405 have no need to include a reflection mirror because there is no component adjacent to the optical scanning devices 405. If the optical scanning devices 405 respectively include a reflection mirror, an overall height of the full-color printer becomes disadvantageously too high. Consequently, any reflection mirror is not used in the optical scanning devices 405 to keep the overall height of the full-color printer in a user-friendly manner.
As described above, when different layouts of image forming apparatuses are produced, it is necessary to produce optical scanning devices having different configurations corresponding to each of the layouts of the image forming apparatuses.
However, although optical scanning devices have different configurations from one another, if the optical scanning devices have the same size of a scanning field (for example, in a case of an A4 paper, 297 mm in a longitudinal direction), the same scanning lens can be used among the optical scanning devices. Therefore, in optical scanning devices produced by the same manufacturer, the same scanning lens is used in common even among different models of optical scanning devices.
Incidentally, to achieve a desired imaging performance, relative positions (layouts) of a light source, a deflector, and a scanning lens in the different models of the optical scanning devices need to be identical with one another regardless of reflection angles of light beams.
In this manner, although some elements can be used in common among different models of optical scanning devices, various types of optical scanning devices are produced in accordance with various layouts of image forming apparatuses as described above, and thus it causes an increase of production costs. Moreover, from a viewpoint of the promotion of recycling, it is not preferable to produce various types of optical scanning devices because it is difficult to reuse the optical scanning devices.